The rotor of a turbomachine typically comprises an impeller secured to a shaft. The impeller may be secured to the shaft by interference fit, which provides a cost-effective means of securement. As the rotor rotates, radial stresses cause the bore of the impeller to expand. As a result, the interference fit between the impeller and shaft decreases. At relatively high speeds, the expansion of the bore may be such that the interference fit is no longer able to transmit the required torque between the shaft and the impeller. In order to avoid this situation, the interference fit between the impeller and the shaft, when stationary, may be increased. However, the required interference fit needed to ensure torque transmission over the full operating speed range of the rotor may exceed the yield point of the impeller. Additionally, the press force required to achieve the required interference fit may be excessive.